The role of opiate receptors located on catecholaminergic cells was studied using primary cultures of adrenal chromaffin cells. These cells contain opiate receptors in measurable amounts. Stimulation of these receptors with agonists decreases the release of catecholamines elicited by nicotine. This effect is stereospecific and is reverted by naloxone and diprenorphine. One of the most potent opiate peptides is met-enkephalin-Arg6-Phe7. This peptide is present in the splanchnic nerve with acetylcholine. Upon release it may function as a cotransmitter for acetylcholine modulating the number of acetylcholine receptors available.